Not Applicable
Not Applicable
Not Applicable
The present invention relates to electronic controls that must determine if a path of an ac circuit is intact or open. Typically this means determining whether a switching component is open or closed, or a whether a functional component is present.
Typically the state of a component that switches an ac load is determined using optoisolators or other active components to interface ac voltages to electronic control level voltages. Alternatively a low voltage switch acting in unison with the ac switch is read by the control to indirectly determine the state of the ac switch. One prior passive component approach with an isolated supply requires a conditioning circuit between ac nodes and works only when the neutral line is the one switched. Other prior passive component approaches only work on supplies that are not isolated from ac. They require a fixed voltage between the control voltages and the ac source.
The approach of using optoisolators or active components requires the use of multiple components for each input to the control. Typically these components include at a minimum an optoisolator, a current limiting resistor on the input and a pull-up resistor on the output. The cost of these components and their assembly add significantly to the cost of electronic controls. The use of active components and the number of components reduce the reliability of this approach.
Using a separate control voltage switch incurs the expense of the switch and the extra connectors and wires to interface it to the control. There is additional expense of mounting hardware and labor. The reliability of mechanical systems is typically far less than a solid state approach.
A technique to interface an electronic control to ac using a resistor, is shown in AN521 of Microchip""s Embedded Control Handbook. In this approach the ground of the control is in common with the ac ground establishing ground as a reference. A resistive connection to hot produces ac source frequency pulses. There is no mention of a means of detecting the state of a node whose connections to hot and/or neutral are not already known. This approach relies on the fixed reference of the common ground that is not present with a floating supply. Proper connections to hot and neutral are assumed. If L1 and neutral were inadvertently reversed in installation the technique will not work.
U.S. Pat. No. 5,202,582 shows a method to determine the state of an ac switch connecting the load to neutral for a floating control using passive components. This approach requires a conditioning circuit with connections to L1, the load side of the switch and a control input. It is designed to determine solely the state of a ground side switch of an ac circuit. The conditioning circuit shapes signal. The shape determines the state of the switch.
This method assumes the correct connections to ac are made during installation, something that is not under the control of the manufacturer. Further this approach requires that neutral be switched leaving the transducers connected to hot unless a L1 side switch is also opened when the door is opened. Finally no method is shown to sense the state of a plurality of ac switches in the same circuit or a plurality of circuits.
U.S. Pat. No. 5,184,026 shows a method that can be used for a plurality of switches. However the method deals with controls whose supply voltages are not isolated from the ac source. Supplies that are not isolated bring the possibility of shock or worse should the operator come in contact with any control voltage. As described the monitoring device requires a reference voltage that is a dc drop from the instantaneously higher of the source lines. To produce such a reference requires multiple components and connections between the source and the control. The monitoring device must include a reactive component to block the dc voltage between the ac node and the control for this approach to work. The reactive components used to block dc alter the phase of signal received by the control.
The present invention connects ac nodes and digital nodes of a control with a floating power supply to determine the state of ac path(s) in the circuit containing the ac nodes. The digital nodes of the present invention are either digital inputs or the supply voltages for the digital circuitry. The connections are made through passive components. The ac potential between the source and the control drives the digital nodes. The subsequent signals on digital nodes are compared to determine the state of ac path(s).
The present invention can determine the state of a plurality of ac paths. The paths may be anywhere in the ac circuit. The state of the path indicates whether it is intact or open. The state of a path can be used to determine the state of a switching means. It can also determine if a functional load component is present. The present invention can also determine if an ac node is floating indicating that all ac paths to the node are open.
The method may be applied to devices where the polarity of the connection to the ac source is unknown. The method may be used to detect zero crossings. The high impedance connections allow inputs to perform other I/O functions when not reading the state of an ac node. The aggregate source-control impedance may be made sufficient to limit the current to a safe level, preferrably below the threshold of sensation, should the operator contact any control node.
The simplest connection, one made by a resistor, is the preferred connection. It ensures that if the digital input has a phase it is the same phase as the driving ac signal. While reactive (energy storing) components may be used in the connections to further distinguish signals they are not required, alter the phase of the signal and add to the cost.
The reliability of the present invention is much greater than the prior approaches given the reduction in the number of interface components. Additionally resistors, the preferred passive component in the connections, are most reliable electrical components.